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I basically agree with @RoboKaren's answer, but wanted to add a couple of things that would take up too much space for a comment.
For starters, you say that the chain mashed up the derailleur. So the derailleur was actually the "victim" of the problem, not necessarily the cause. So while you might need to replace the derailleur, that is likely not the only ...

If your bicycle is a BSO (bicycle shaped object sold at discount mass retailers), then likely no. You'd spend $100+ labor on the derailleur and a new chain, but then the next week the brakes would fail, the handlebar would come off, or the frame would crack. BSOs are money pits. Furthermore, it's unlikely you could just replace the derailleur, you'd have to ...

A 11 speed cassette would mean a new hub (probably a new wheel realistically) and likely a new derailleur to match the cable pull of the STI shifters plus the labor (this includes installation of the new cable stops, new cables, re-wrapping the bar after putting on the new brifters, etc.). You will also need to spread the frame to get a modern hub in there, ...

You mentioned long distance ridding. Here is what I would be thinking about:
Comfort
When I think about comfort there are two things that I think about. Most importantly I think about handlebars and more specifically how many places you have to put your hands. Drop bars are nice because you get three positions, but I don't like drops when I am riding ...

From the pictures you've posted across a few different questions, I can almost guarantee you will not make money selling that bike, no matter what you do to it. At the very least you will need a new freewheel and chain, new tyres, cables, and brake pads. Sadly, those will probably set you back more than you could sell the bike for. Given your apparent lack ...

Your current bike has decent wheels and reasonable components. If they have been maintained well I don't think you'll see much difference there other than 10spd gearing. The big change to a new bike in that price range will be the frame.
It is much easier now to get a frame that actually fits your riding style, I see you have an adjustable angle stem. ...

TL; DR: There is going to be a lot of difference. A 1500 Euro bike today would probably be comparable to a 6-7000 Euro bike from 10 years ago.
Elaboration:
There are going to be quite a few improvements in the bike due to technology advances and research and development. Some of the base models will not be radically different from your frame, although even ...

The two upgrades which make the biggest difference are the wheels and the frame itself. (I know, better shifting is fun but it won't change your speed/distance much) You could also look at getting better tires, but since you have a commuting bike they should already be fine.
Given the price of a good wheel set you might be better off with a complete bike. ...